Chesterton is talking about social institutions and social change, not unconscious acts and biological evolution. His principle doesn't apply at all here. He's

Chesterton is talking about social institutions and social change, not unconscious acts and biological evolution. His principle doesn't apply at all here. He's asserting that every long-standing social institution very likely came to exist to serve some purpose, so if one says we should scrap institution X because it's useless, it's likely one is wrong. This has nothing to do with man's biological evolution. In fact we have a myriad of "bad features" (congenital diseases, disabilities, cancer) that have survived evolution.